Clot retrieval device with flexible collapsible frame

ABSTRACT

A clot retrieval device includes an inner expandable member and an outer expandable member, each formed from respective strut frameworks such that the outer expandable member has larger cell openings than the inner expandable member. The outer expandable member can have multiple discontinuous body segments spaced apart in relation to a longitudinal axis of the device. Adjacent discontinuous body segments can be joined by a pair of tapered connecting arms that are able to bend with a small radius of curvature compared to the body segments. Some or all of the body segments can include radiopaque markers positioned to illustrate a circumference of the respective body segment and slightly staggered in relation to a longitudinal axis of the device such that the markers nest when the device is collapsed for delivery.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patent application Ser. No. 16/946,464 filed Jun. 23, 2020. The entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to devices and methods of removing acute blockages from blood vessels. More specifically, the invention relates to removing obstructions from cerebral arteries in patients suffering acute ischemic stroke (AIS), from pulmonary arteries in patients suffering from pulmonary embolism (PE), from coronary native or graft vessels in patients suffering from myocardial infarction (MI), and from other peripheral arterial and venous vessels in which a clot or other obstruction (e.g. misplaced device, migrated device, large emboli, etc.) is causing an occlusion.

BACKGROUND

Thromboembolism occurs when part or all of a thrombus breaks away from the blood vessel wall. This clot (now called an embolus) is then carried in the direction of blood flow. An ischemic stroke may result if the clot lodges in the cerebral vasculature. A pulmonary embolism may result if the clot originates in the venous system or in the right side of the heart and lodges in a pulmonary artery or branch thereof. Clots may also develop and block vessels locally without being released in the form of an embolus—this mechanism is common in the formation of coronary blockages.

There are a number of access challenges that make it difficult to deliver treatment devices to a clot or other obstruction. In cases where access involves navigating the aortic arch (such as coronary or cerebral blockages) the configuration of the arch in some patients makes it difficult to position a guide catheter. These difficult arch configurations are classified as either type 2 or type 3 aortic arches with type 3 arches presenting the most difficulty. The tortuosity challenge is even more severe in the arteries approaching the brain. For example, it is not unusual at the distal end of the internal carotid artery that the device will have to navigate a vessel segment with a 180° bend, a 90° bend and a 360° bend in quick succession over a few centimeters of vessel. In the case of pulmonary embolisms, access may be gained through the venous system and then through the right atrium and ventricle of the heart. The right ventricular outflow tract and pulmonary arteries are delicate vessels that can easily be damaged by inflexible or high profile devices. For these reasons it is desirable that an obstruction retrieval device be compatible with a delivery catheter having a low profile and high flexibility.

The vasculature in the area in which the clot may be lodged is often fragile and delicate. For example, neurovascular vessels are more fragile than similarly sized vessels in other parts of the body and are in a soft tissue bed. Excessive tensile forces applied on these vessels could result in perforations and hemorrhage. Pulmonary vessels are larger than those of the cerebral vasculature, but are also delicate in nature, particularly more superior vessels.

The clot may comprise any of a range of morphologies and consistencies. Long strands of softer clot material may tend to lodge at bifurcations or trifurcations, resulting in multiple vessels being simultaneously occluded over significant lengths. More mature and organized clot material is likely to be less compressible than softer fresher clot, and under the action of blood pressure it may distend the compliant vessel in which it is lodged.

The clots may not only range in shape and consistency, but also may vary greatly in length, even in any one given area of the anatomy. For example, clots occluding the middle cerebral artery of an ischemic stroke patient may range from just a few millimeters to several centimeters in length.

Stent-like clot retrievers are being increasingly used to remove clot and other obstructions from cerebral vessels of acute stroke patients. These are self-expanding devices, similar in appearance to a stent attached to the end of a long shaft and are advanced through a microcatheter and deployed across clot obstructions in order to trap and retrieve them. They rely on a pinning mechanism to grab the clot by trapping the clot between the self-expanding stent-like body and the vessel wall.

Typically, a stent-like clot retriever relies on its outward radial force (RF) to retain its grip on the clot. If the RF is too low the stent-like clot retriever will lose its grip on the clot, but if the RF is too high the stent-like clot retriever may damage the vessel wall and may require too much force to withdraw. Because clots vary in morphology across patients, the RF required to grip the clot also varies. Because blood vessel fragility and geometry also varies across patients, the RF required to reduce the risk of vessel trauma also varies.

In some treatments, some known stent-like clot retriever designs can lose their grip on a clot when withdrawn proximally around a bend in a tortuous vessel. This typically occurs because the struts of the stent-like clot retriever are placed in tension when it is retracted. This tension is due to friction between the device and the blood vessel and is increased if an additional load is applied load such as that provided by a clot. In a bend the struts on the outside of the bend are placed in higher tension than those on the inside. In order to attain the lowest possible energy state, the outside surface of the stent moves towards the inside surface of the bend, which reduces the tension in the struts, but also reduces the expanded diameter of the stent-like clot retriever.

Some treatments rely on pinning the clot between the stent-like clot retriever and the vessel wall and thus may not restrain the clot effectively when passing a branch vessel or when passing into a vessel that is larger than the fully expanded diameter of the stent-like clot retriever. Pinning the clot between the stent-like clot retriever and the vessel wall in order to remove it from the vessel also results in high shear forces against the side of the clot as it is removed, potentially releasing fragments of the clot. If these fragments are not retained by the device, they may be released leading to further blockages in the distal vasculature.

In some treatments, the stent-like clot retriever may be shorter than the clot itself. A device that is shorter than the clot is unlikely to be able to restore flow through the occluded area upon deployment, and thus the pressure gradient across the clot remains a significant impediment to its removal. Simply making such a device longer would likely render it difficult to track through tortuous anatomies and could be traumatic to the vasculature, taking more force to withdraw and potentially getting stuck and requiring surgery to remove.

For many reasons including some or all of the above limitations it is often necessary for a physician to make multiple passes with a clot retrieval device in order to fully remove an obstructive clot. However, each time a clot retrieval device is withdrawn the access to the target site is lost. The initial access steps of placing the large bore catheter do not need to be repeated as it remains in place after the initial clot retrieval attempt. Only the steps of accessing the clot site after the large bore catheter has been placed need to be repeated. Thus, it is necessary to re-advance a guidewire and microcatheter to access and re-cross the clot, and then remove the guidewire and advance the clot retrieval device through the microcatheter. Navigating the guidewire and microcatheter to the clot can take a considerable amount of time, especially if the vessels are tortuous. This additional time and device manipulation all adds to the risks to which the patient is exposed.

SUMMARY

Examples disclosed herein generally include a clot retrieval device having an inner expandable member and an outer expandable member, each formed from respective strut frameworks such that the outer expandable member has larger cell openings than the inner expandable member. The outer expandable member can have multiple discontinuous body segments spaced apart in relation to a longitudinal axis of the device. Adjacent discontinuous body segments can be joined by a pair of tapered connecting arms that are able to bend with a small radius of curvature compared to the body segments. This small radius of curvature can have a range of values depending on the tortuosity of the vasculature the device is expanded in. It will approximately equal 0 mm when the device is in a straight vessel and will approximately equal 0.5 mm when the device is in a vessel with a 180-degree bend. Some or all of the body segments can include radiopaque markers positioned to illustrate a circumference of the respective body segment and slightly staggered in relation to a longitudinal axis of the device such that the markers nest when the device is collapsed for delivery.

An example clot retrieval device has a collapsed configuration and an expanded configuration. The clot retrieval device is configured to remove clot from a blood vessel. The clot retrieval device has an inner expandable member and an outer expandable member. The inner expandable member has a first framework of struts and the outer expandable member has a second framework of struts. The second framework at least partially radially surrounds the inner expandable member.

Closed cells of the second framework of the outer expandable member can be larger than closed cells of the first framework of the inner expandable member.

The outer expandable member can have a first and a second body segment connected by two connecting arms, wherein the first body segment is positioned in a proximal direction in relation to the second body segment. Each of the two connecting arms respectively can have a tapered shape that is wider where the arm is near the first, proximal body segment and narrower where the arm is near the second, distal body segment. As shown in FIG. 1B and FIG. 4C, approximate values for the labelled dimensions are as follows; the height ‘H’ has a value of 0.075 mm, the strut width ‘W1’ has a value of 0.16 mm, the strut width ‘W2’ has a value of 0.08 mm and the strut width ‘W3’ has a value of 0.20 mm. Hence, the approximate percentage change in width between ‘W1’ and ‘W2’ is a decrease of 50% and the approximate percentage change in width between ‘W2’ and ‘W3’ is an increase of 60%. The outer expandable member can have additional body segments connected to the first and/or second body segment by additional connecting arms.

The outer expandable member can have at least two inlet mouths in the second framework including a pair of inlet mouths between the first and second body segments. Each of the two inlet mouths between the first and second body segment can have a respective opening bounded by the first body segment, the second body segment, and the two connecting arms.

The first body segment can have at least two pairs of struts each terminating in a respective distal apex and forming a proximal boundary of a respective inlet mouth of the two inlet mouths.

The two connecting arms between the first and second body segments of the outer expandable member can extend substantially parallel to a longitudinal axis of the device.

The two connecting arms between the first and second body segments of the outer expandable member can be positioned approximately 180° from each other about a circumference of the outer expandable member.

The first body segment and the second body segment can be connected to each other solely via the two connecting arms.

Each of the two connecting arms can be configured to bend with a curvature having a radius smaller than a radius of curvature of a majority of struts of the first body segment and the second body segment as the clot retrieval device is pulled proximally through a tubular vasculature comprising a bend of about 180°.

The outer expandable member can have three or more body segments each shaped substantially similarly to the first body segment and the second body segment. The outer expandable member can include pairs of tapered connecting arms such that each respective pair of tapered connecting arms joins longitudinally adjacent body segments of the three or more body segments. The tapered connecting arms can be shaped and oriented similarly to the connecting arms between the first and second body segments.

One or both of the first and second body segments can respectively include four or more radiopaque markers positioned around a circumference of the respective body segment. When the clot retrieval device is in the collapsed configuration, each of the radiopaque markers can be offset from adjacent radiopaque markers of the four or more radiopaque markers. The markers can be offset from adjacent radiopaque makers in relation to a longitudinal axis of the device. When the clot retrieval device is in the collapsed configuration, alternating radiopaque markers of the four or more radiopaque markers can be aligned in a plane orthogonal to the longitudinal axis.

The first body segment can include a first set of four or more radiopaque markers. The second body segment can include a second set of four or more radiopaque markers. When the clot retrieval device is in the expanded configuration, the first and second sets of four or more radiopaque markers are spaced approximately 8 millimeters apart, measured in the direction of the longitudinal axis. When the clot retrieval device is in the collapsed configuration, the first and second sets of four or more radiopaque markers are spaced approximately 10 millimeters apart, measured in the direction of the longitudinal axis.

Each of the four or more radiopaque markers can include radiopaque material positioned in an eyelet.

At least two of the four or more radiopaque markers can be aligned, in the direction of the longitudinal axis, with a respective connecting arm of the two connecting arms.

Another example clot retrieval device can have a collapsed configuration and an expanded configuration. The clot retrieval device is configured to remove a clot from a blood vessel. Structures and functionality of this example clot retrieval device are combinable with structures and features of the previous example clot retrieval device.

The example clot retrieval device includes an inner expandable member having a first framework of struts and an outer expandable member having a second framework of struts. The second framework of struts can form closed cells larger than closed cells of the first framework of inner expandable member. The second framework can at least partially radially surround the first framework of the inner expandable member.

The example clot retrieval device can include four or more radiopaque markers affixed to the second framework of struts and positioned to indicate a circumference of the outer expandable member. The radiopaque markers can be further positioned such that when the clot retrieval device is in the collapsed configuration, each of the radiopaque markers is offset, in relation to a longitudinal axis of the device to respective circumferentially adjacent radiopaque markers.

The outer expandable member can include discontinuous body segments spaced apart from each other in the direction of the longitudinal axis. The radiopaque markers can be positioned to indicate a circumference of a body segment of the discontinuous body segments.

The example clot retrieval device can include a first body segment and a second body segment, wherein the first body segment is positioned in a proximal direction in relation the second body segment. The outer expandable member can include two connecting arms joining the first body segment to the second body segment. Each of the two connecting arms can respectively have a tapered shape that is wider near the proximal, first body segment and narrower near the distal, second body segment.

At least two of the four or more radiopaque markers can be aligned, in the direction of the longitudinal axis, with a respective connecting arm of the two connecting arms.

The outer expandable member can include two inlet mouths in the second framework. Each of the two inlet mouths can include a respective opening bounded by the first body segment, the second body segment, and the two connecting arms.

The first body segment can include the four or more radiopaque markers forming a first set of markers, and the second body segment can include a second set of four or more radiopaque markers positioned to indicate a circumference of the second body segment. The second set of radiopaque markers can be positioned such that when the clot retrieval device is in the collapsed configuration, each of the radiopaque markers of the second set is offset, in relation to a longitudinal axis of the device to respective adjacent radiopaque markers of the second set. Markers in the first set of radiopaque markers can be similarly offset.

The two connecting arms can be positioned approximately 180° from each other about a circumference of the outer expandable member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an isometric view of an example clot retrieval device according to aspects of the present invention.

FIG. 1B shows a close-up of a portion of the clot retrieval device illustrated in FIG. 1A, the portion including a tapered strut according to aspects of the present invention.

FIG. 2A shows a plan view of a first side of the clot retrieval device illustrated in FIG. 1A.

FIG. 2B shows the view clot retrieval device as illustrated in FIG. 2A having an inner expandable member of the clot retrieval device removed from the illustration.

FIG. 2C shows the view of the clot retrieval device as illustrated in FIG. 2A having an outer expandable member of the clot retrieval device removed from the illustration.

FIG. 3A shows a plan view of a second side of the clot retrieval device illustrated in FIG. 1A, the second side viewed at 90° from the first side view illustrated in FIG. 2A.

FIG. 3B shows the view clot retrieval device as illustrated in FIG. 3A having the inner expandable member of the clot retrieval device removed from the illustration.

FIG. 3C shows the view of the clot retrieval device as illustrated in FIG. 3A having the outer expandable member of the clot retrieval device removed from the illustration.

FIG. 4A shows a linear view of the outer expandable member of the clot retrieval device cut along a centerline indicated in FIGS. 2B and 3B and flattened.

FIG. 4B shows a close-up of a portion of the outer expandable member of the clot retrieval device as indicated in FIG. 4A.

FIG. 4C shows a close-up of a portion of the outer expandable member of the clot retrieval device as indicated in FIG. 4B.

FIG. 5A shows a plan view of a distal end of the clot retrieval device illustrated in FIG. 1A.

FIG. 5B shows the view clot retrieval device as illustrated in FIG. 5A having the inner expandable member of the clot retrieval device removed from the illustration.

FIG. 5C shows the view of the clot retrieval device as illustrated in FIG. 5A having the outer expandable member of the clot retrieval device removed from the illustration.

FIG. 6A shows an isometric view of another example clot retrieval device according to aspects of the present invention.

FIG. 6B shows a close-up of a portion of the clot retrieval device illustrated in FIG. 6A, the portion including a tapered strut according to aspects of the present invention.

FIG. 7A shows a plan view of a first side of the clot retrieval device illustrated in FIG. 6A.

FIG. 7B shows the view clot retrieval device as illustrated in FIG. 7A having an inner expandable member of the clot retrieval device removed from the illustration.

FIG. 7C shows the view of the clot retrieval device as illustrated in FIG. 7A having an outer expandable member of the clot retrieval device removed from the illustration.

FIG. 8A shows a plan view of a second side of the clot retrieval device illustrated in FIG. 6A, the second side viewed at 90° from the first side view illustrated in FIG. 7A.

FIG. 8B shows the view clot retrieval device as illustrated in FIG. 8A having the inner expandable member of the clot retrieval device removed from the illustration.

FIG. 8C shows the view of the clot retrieval device as illustrated in FIG. 8A having the outer expandable member of the clot retrieval device removed from the illustration.

FIG. 9 shows a linear view of the outer expandable member of the clot retrieval device cut along a centerline indicated in FIGS. 7B and 8B and flattened.

FIG. 10A shows a plan view of a distal end of the clot retrieval device illustrated in FIG. 6A.

FIG. 10B shows the view clot retrieval device as illustrated in FIG. 10A having the inner expandable member of the clot retrieval device removed from the illustration.

FIG. 10C shows the view of the clot retrieval device as illustrated in FIG. 10A having the outer expandable member of the clot retrieval device removed from the illustration.

FIG. 11A shows an example outer expandable member traversing a lumen having a 360° bend according to aspects of the present invention.

FIG. 11B shows a close-up of a portion of the outer expandable member as indicated in FIG. 11A.

FIG. 12A shows an illustration of a portion of an example expandable member having a radiopaque marker according to aspects of the present invention.

FIG. 12B shows a side view of the portion of the expandable member illustrated in FIG. 12A.

FIGS. 13A and 13B are radiographic images of an example clot retrieval device according to aspects of the present invention.

FIG. 14 shows an illustration of an alternative distal portion of an example clot retrieval device according to aspects of the present invention.

DETAILED DESCRIPTION

Specific embodiments of the present invention are now described in detail with reference to the figures, wherein identical reference numbers indicate identical or functionality similar elements. The terms “distal” or “proximal” are used in the following description with respect to a position or direction relative to the treating physician. “Distal” or “distally” are a position distant from or in a direction away from the physician. “Proximal” or “proximally” or “proximate” are a position near or in a direction toward the physician.

Accessing cerebral, coronary and pulmonary vessels involves the use of a number of commercially available products and conventional procedural steps. Access products such as guidewires, guide catheters, angiographic catheters and microcatheters are described elsewhere and are regularly used in catheter lab procedures. It is assumed in the descriptions below that these products and methods are employed in conjunction with the device and methods of this invention and do not need to be described in detail.

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in many cases in the context of treatment of intracranial arteries, the invention may also be used in other body passageways as previously described.

FIG. 1A shows a distal portion of an example clot retrieval device 100 in an expanded configuration. The clot retrieval device 100 generally extends to define a longitudinal axis A-A and has a distal coil 108 at its distal end, an outer expandable member 102 and an inner expandable member 103 extending proximally and coaxially from the distal coil 108, and a proximal coil 104 extending proximally from the outer expandable member 102 and the inner expandable member 103. The device 100 can include additional features such as an elongate shaft 106, a sleeve 105, and indicator bands 107. The device 100 can include a distal junction or collar 109 joining the distal coil 108 to the outer expandable member 102 and the inner expandable member 103. The device 100 can include a proximal junction or collar 112 joining the proximal coil 104 to the outer expandable member 102 and the inner expandable member 103. The junctions 109, 112 can be constructed as usable with a clot retrieval device having two expandable layers 102, 103 such as described in U.S. Pat. No. 10,390,850 incorporated herein by reference as if set forth herein in its entirety.

FIG. 1B shows a close-up of a portion of the clot retrieval device illustrated in FIG. 1A, the portion including a tapered strut according to aspects of the present invention.

FIG. 2A shows a plan view of a first side of the clot retrieval device 100. FIG. 2B shows the view clot retrieval device 100 as illustrated in FIG. 2A having the inner expandable member 103 removed for the purpose of illustration. FIG. 2C shows the view of the clot retrieval device 100 as illustrated in FIG. 2A having the outer expandable member 102 removed for the purpose of illustration. FIG. 3A shows a plan view of a second side of the clot retrieval device 100, the second side viewed at 90° from the first side view illustrated in FIG. 2A. FIG. 3B shows the view clot retrieval device 100 as illustrated in FIG. 3A having the inner expandable member 103 removed for the purpose of illustration. FIG. 3C shows the view of the clot retrieval device 100 as illustrated in FIG. 3A having the outer expandable member 102 removed for the purpose of illustration. FIG. 4A shows a linear view of the outer expandable member 102 cut along a line B-B indicated in FIGS. 2B and 3B and flattened. FIG. 4B shows a close-up of a portion of the outer expandable member 102 as indicated in FIG. 4A. FIG. 4C shows a close-up of a portion of the outer expandable member 102 as indicated in FIG. 4B. FIG. 5A shows a plan view of a distal end of the clot retrieval device 100. FIG. 5B shows the view of the clot retrieval device 100 as illustrated in FIG. 5A having the inner expandable member 103 removed for the purpose of illustration. FIG. 5C shows the view of the clot retrieval device 100 as illustrated in FIG. 5A having the outer expandable member 102 removed for the purpose of illustration.

As described in greater detail in relation to FIGS. 1B and 4C, the outer expandable member 102 can include tapered struts 129, 130 joining body segments 126, 127, 128. The tapered struts 129, 130 are shaped to provide flexibility to the outer expandable member 102 to facilitate withdraw of the device 100 from tortuous vascular when an obstruction is at least partially confined by the outer expandable member 102. Additionally, or alternatively, the tapered struts 129, 130 are shaped to promote apposition of the outer expandable member 102 circumferentially to blood vessel walls as the device 100 is withdrawn through tortuous vasculature when an obstruction is at least partially confined by the outer expandable member 102.

As described in greater detail in relation to FIGS. 4A and 4B, the outer expandable member 103 can include staggered radiopaque markers positioned to facilitate visualization of the device 100 during treatment while also maintaining a small profile collapsed configuration of the outer expandable member 102 to facilitate traverse of the collapsed device 100 across a clot or other obstruction.

Referring collectively to FIGS. 1A through 5C, the outer expandable member 102 and inner expandable member 103 are collapsible into a restraining sheath (e.g. microcatheter) sized to traverse a clot or other obstruction. The outer expandable member 102 and inner expandable member 103 are each configured to self-expand upon release from the restraining sheath. In the expanded configuration, the device 100 can facilitate clot retrieval, flow restoration, and/or fragmentation protection.

Both the inner and outer expandable members 102, 103 are preferably made from a material capable of recovering its shape automatically once released from a constricted delivery configuration. A super-elastic or pseudo-elastic material such as Nitinol or an alloy of similar properties is particularly suitable. The material can have a high recoverable strain sufficient to resiliently collapse and expand as described herein. The material could be in many forms such as wire or strip or sheet or tube. A particularly suitable manufacturing process is to laser cut a Nitinol tube and then heat set and electropolish the resultant structure to create a framework of struts and connecting elements. This framework can be any of a huge range of shapes as understood by a person skilled in the pertinent art according to the teachings disclosed herein. The framework may be rendered visible under fluoroscopy through the addition of alloying elements or through a variety of other coatings or marker bands. For instance, the framework can include material and/or markers with radiopaque material including, but not limited to Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride, Gold, Tungsten, Platinum, Iridium, Tantalum, and alloys thereof. Specifically, in some examples, the framework can include radiopaque markers having an Iridium alloy, and more specifically a Platinum-Iridium alloy.

The inner expandable member 103 is preferably configured to expand to a lesser diameter D2 than that of the smallest vessel in which it is intended to be used. This diameter D2 is typically less than 50% that of the diameter D1 of the outer expandable member 102 and may be as low as 20% or less of the outer member diameter D1.

A distal scaffolding zone can incorporate strut elements from the framework of the outer and/or inner expandable members 102, 103 such as an expanded portion 110 of the inner expandable member 103 and a distal portion 128 of the outer expandable member 102. The strut geometry of the distal scaffolding zone can be shaped as illustrated herein, or as described in relation to compatible stent-like clot retrievers, including but not limited to as disclosed in U.S. Pat. No. 10,390,850. The distal scaffolding zone can further include fine wires or fibers to provide added scaffolding with minimal impact of overall device profile or deliverability. Suitable materials ideally have a high tensile strength so that a very fine wire or fiber with sufficient integrity for manufacturability and use can be produced, such as for example polymer materials like UHMWPE, Aramid, LCP, PET or PEN, or metals such as Tungsten, MP35N, stainless steel or Nitinol.

In each of the expanded configuration and the collapsed configuration, the inner expandable member 103 and outer expandable members define respective tubular bodies. Preferably the tubular bodies are coaxial about the longitudinal axis A-A. The device 100 includes a reception space 111 within the outer expandable member 102 and outside the inner expandable member 103 when the inner and outer expandable members 102, 103 are in the expanded configuration. The device 100 and reception space 111 are sized, shaped, and otherwise configured to allow a clot to become at least partially confined within the reception space during a clot removal treatment. The interior of the inner expandable member 103 when expanded is configured to provide a flow path through which blood can flow when the device 100 is expanded through a clot.

During a clot removal treatment, the length of the outer expandable member 102 can be about as long as the length of the occlusive clot or longer to remove many of the degrees of freedom of movement otherwise available to the clot. The outer expandable member 102 includes inlet mouths 222 sized, shaped, another otherwise configured to provide the primary freedom of movement available to the clot and so the expansion of the outer expandable member 102 urges the clot into the reception space 111. The outer member 102 has multiple inlet mouths 122 to accept the clot. In this way inlet mouths 122 allow portions of the clot to enter reception space 111 of the outer expandable member 102, and thus allow the clot to be retrieved without being excessively compressed. This is advantageous because the inventors have discovered that compression of clot causes it to dehydrate, which in turn increases the frictional properties of the clot, and increases its stiffness, all of which makes the clot more difficult to disengage and remove from the vessel. This compression can be avoided if the clot migrates inward through the scaffolding of the outer expandable member 102 as the scaffolding migrates outward towards the vessel wall.

The inlet mouths 122 can further allow the outer expandable member 102, when retracted, to apply a force to the clot in a direction substantially parallel to the direction in which the clot is to be pulled from the vessel (i.e. substantially parallel to the central axis of the vessel). This means that the outward radial force applied to the vasculature may be kept to a minimum, which in turn means that the action of the clot retrieval device 100 on the clot does not serve to increase the force required to dislodge the clot from the vessel, thus protecting delicate cerebral vessels from harmful radial and tensile forces.

The outer expandable member 102 includes proximal struts 120 connected at their proximal ends to the proximal collar 112 and at their distal ends to a proximal body segment 126. The proximal struts 120 can have a tapered profile or be otherwise configured to provide a gradual stiffness transition from the shaft 106 to the tubular body of the outer expandable member 102.

The proximal body segment 126 is connected to a middle body segment 127 by two connecting arms 129, which run from a proximal junction 139 to a distal junction 140. The middle body segment 127 is in turn connected to a distal body segment 128 by two connecting arms 130, which run from a proximal junction 141 to a distal junction 142. The region between the middle and distal body segments 127, 128 includes two inlet mouths 122 through which the clot may pass and enter the reception space 111 defined by the region between the inner and outer members 102, 103.

As illustrated in greater detail in FIGS. 1B and 4C, each of the connecting arms 129 can have a tapered profile with a width that tapers from a wider dimension W1 at the respective proximal junction 139, 141 to a narrower width W2 near the respective distal junction 140, 142. At the distal junction 140, 142, the connecting arms 129, 130 can expand to a width W3 that is wider than the narrower width W2 to accommodate branching distal struts 170. The connecting arms 129, 130 can have a height H (thickness) that is substantially uniform. The height H can be consistent with the strut thickness of the majority of the outer expandable member 102.

In one example, as shown in FIG. 1B and FIG. 4C, approximate values for the labelled dimensions are as follows; the height H has a value of about 0.075 mm, the proximal strut width W1 has a value of about 0.16 mm, the distal strut width W2 has a value of about 0.08 mm and the bifurcation strut width W3 has a value of about 0.20 mm. Hence, the approximate percentage change in width between the proximal width W1 and the distal width W2 is a decrease of 50% and the approximate percentage change in width between the distal width W2 and the bifurcation width W3 is an increase of 60%.

The tapered shape of the connecting arms 129, 130 can be configured to bend to reduce withdrawal force around blood vessel bends compared to a similarly constructed stent-like clot retriever device having non-tapered connecting arms. The arms 129, 130 can be configured to bend with a curvature having a larger curvature (smaller radius of curvature) compared to a majority of struts within the outer expandable member 102. (See radius r as illustrated in FIG. 11B.)

The connecting arms 129 between the proximal body segment 126 and the middle body segment 127 of the outer expandable member 102 can be substantially aligned with the connecting arms 130 between the middle and distal body segments 127, 128 to align the neutral axis of the body segments 126, 127, 128 during bending. In another embodiment the connecting arms 129 between the proximal body segment 126 and the middle body segment 127 can be aligned at an angle, such as 90° to the connecting arms 130 between the middle and distal body segments 127, 128.

As illustrated in greater detail in FIGS. 2B and 3B, the proximal body segment 126 includes interconnected struts, with certain struts such as strut 143 terminating in a distal apex 133 with no distal connecting elements, and other struts such as 144 terminating in junction points 145, 146. The middle body segment 127 includes interconnected struts, with certain struts such as strut 147 terminating in a distal apex 134 with no distal connecting elements, and other struts such as strut 148 terminating in junction points 171.

One or more of the body segments 126, 127, 128 can include marker bands or radiopaque features such as gold or platinum marker or coils. In the illustrated embodiment, oval markers 121, 125 are shown fixed in eyelets on struts on the proximal, middle, and distal body segments 126, 127, 128. The markers 125 on the distal body segment 128 can be positioned to indicate to the user the position of the distal body segment 128 and therefore distal portion of the device 100 to aid in accuracy of deployment of the device 100. The distal body segment 128 can include a single marker 125 to indicate the position of the distal body segment 128, or multiple markers to indicate a circumference of the distal body segment 128. Each of the proximal and middle body segments 126, 127 can include multiple oval markers 121 positioned circumferentially around the respective body segment 126, 127 to indicate to the user the expanded circumference C1 and/or position of the respective body segments 126, 127 during a treatment (where the circumference C1 is the diameter D1 times pi). In the illustrated embodiment, each of the proximal and middle body segments 126, 127 includes four markers 121 positioned approximately equidistant around a circumference C1 of the outer expandable member 102.

FIGS. 4A and 4B illustrate the outer expandable member 102 cut along the line B-B as indicated in FIGS. 2B and 3B, laid flat, and collapsed to a height C2 corresponding to a circumference of the outer expandable member 102 when the device 100 is constrained by a microcatheter or sheath. As illustrated in greater detail in FIG. 4B, the markers 121 on each of the proximal body segment 126 and the middle body segment 127 are staggered, offset in the direction of the longitudinal axis A-A (i.e. positioned at different distances from the proximal collar 112) to facilitate collapse of the height C (circumference) of the outer expandable member 102. Each of the respective markers 121 connect to an elongated segment 172 which is shaped to nest the adjacent markers 121 between a junction (e.g. junction 141) and the respective connected marker 121. The elongated segments 172 and markers 121 are positioned in an alternating fashion circumferentially.

The struts in the body segments 126, 127, 128 can be configured so that during loading, crowns or junctions (e.g. junction 145 and junction 150 and other similarly shaped junctions) do not align at the same distance from the proximal collar. During loading or re-sheathing, a higher force is generally required to load a junction (crown) than a strut into the sheath, therefore if multiple crowns are loaded at the same time the user may notice an increase in loading force. By offsetting the crowns by making alternative struts 144 and 151 different lengths the loading force may be reduced and the perception to the user is improved.

The distal end of the distal body segment 128 includes struts forming a tapered shape terminating at the distal junction point 109, thus defining a closed end distal to the outer member 102. The distal body segment 128 is viewed from the distal end of the device 100 in a planar view in FIG. 5A with the inner expandable member 103 removed in FIG. 5B for the purposes of illustration and the outer expandable member 102 removed in FIG. 5C for the purposes of illustration. The distal end of the distal body segment 128 can include a distal framework as illustrated herein, or an alternative distal framework usable with a stent-like clot retriever device. The tapered portion of the distal body segment 128 can be shaped and otherwise configured to prevent egress of clot or clot fragments that have entered the reception space 111 between the inner and outer expandable members 102, 103. The expanded distal struts 110 of the inner expandable member 103 act as an additional three dimensional filter in combination with the closed end of the outer expandable member 102 to further prevent the egress of clot or clot fragments. In certain embodiments this distal section may comprise fiber attachment points such as eyelets or other fiber attachment features and fibers may be connected to the distal section at these attachment points to create a distal net.

As illustrated in greater detail in FIGS. 2C, 3C, and 5C, the inner expandable member 103 is configured to self-expand upon release from a restraining sheath (such as a microcatheter) to a diameter D2 that is larger than the expanded diameter D1 of the outer expandable member 102 and smaller than a diameter of a blood vessel that the device 100 is configured to treat. The inner expandable member 103 includes a scaffolding that is denser, having smaller openings, compared to the outer expandable member 102. The inner expandable member 103 is configured so as to provide a flow lumen through the device 100 to facilitate the immediate restoration of blood flow past the clot upon deployment. Additionally, or alternatively, the inner expandable member 103 is configured to scaffold said flow lumen through the clot to prevent the liberation of fragments which might otherwise lodge in the distal vasculature. The inner expandable member 103 includes connected struts 131 that may contact a clot when initially deployed in a target vessel within the clot. The contact of the struts 131 of the inner expandable member 103 with the clot can provide additional grip and can assist in the initial dislodgement of the clot from the vessel when the device is retracted.

Inner expandable member 103 includes a generally cylindrical section of interconnected struts 131, which is connected at its proximal end by a strut 138 (or multiple struts) to the proximal junction 112. The distal end of the inner expandable member 103 includes of an expansile section formed from expanded struts 110 which have a diameter greater than the diameter D2 of the body section of the inner expandable member 103. These expanded struts 110 are connected to a coil section 118 which in this embodiment is laser cut from the tubing that the inner expandable member 103 is also cut from during processing.

The shaft 106 can include a tapered wire shaft, and may be made of stainless steel, MP35N, Nitinol or other material of a suitably high modulus and tensile strength. Shaft 106 may have indicator bands 107 on the shaft to indicate to the user when the distal end of the device is approaching the end of the microcatheter during insertion. These bands are positioned so that as they approach a microcatheter hub or hemostasis valve, they indicate the distal tip of the device is approaching the end of the microcatheter. These indicator bands can be formed by printing or removing or masking areas of shaft coating so that they are visually differentiated from the remainder of the shaft. The indicator bands 107 can additionally be recessed below the surface of the shaft 106 to give tactile feedback to the user as they approach the microcatheter.

The proximal coil 104 can extend from a distal portion of the shaft 106. The proximal coil 104 can be metallic and may be formed from stainless steel or from a more radiopaque material such as platinum or gold for example or an alloy of such a material. Additionally, or alternatively, the coil may be coated with a low friction material or have a polymeric jacket positioned on the outer surface of the coil. Adjacent to this coil 104 a sleeve 105 may be positioned on shaft 106. This sleeve 105 can include polymeric material and may be positioned over the tapered section of the shaft. The sleeve 105 may be rendered radiopaque through the addition of a filler material such as tungsten or barium sulphate. The sleeve 105 and shaft 106 may be coated with a material to reduce friction and thrombogenicity. The coating may consist of a polymer, a low friction lubricant such as silicon, a hydrophilic or a hydrophobic coating. This coating may also be applied to the outer expandable member 102 and inner expandable member 103.

The outer expandable member 102 and the inner expandable member 103 can joined at the proximal junction 112 and the distal junction 109 during assembly. To minimize tension within the expandable members 102, 103 during use, the length of the outer expandable member 102 can be substantially the same as the length of the inner expandable member 103 in the freely expanded configuration and the collapsed, loaded configuration. The expanded struts 110 of the inner expandable member 103 elongate during loading so that the lengths of the inner and outer expandable members are equal when fully loaded in a microcatheter. Length differentials between the inner expandable member 103 and the outer expandable member 102 can still occur when the device is deployed in a small vessel or during the loading or deployment process. The coil 118 at the distal end of the inner expandable member 103 can accommodate minor length differentials by stretching without applying significant tensile or compressive forces to the device. In another embodiment this coil 118 could be formed separately to the inner expandable member 103 and then be assembled to it. The coil 118 can be formed from a stainless steel material, a polymer or from a more radiopaque metal such as gold or platinum or an alloy of such a material. The coil 118 can also be replaced with a longitudinal length of an elastic material such as a low modulus polymer or elastomer.

In other embodiments the inner expandable member 103 may not be connected to the distal end of the outer expandable member 102 at all or may be constrained within the outer expandable member 102 without being fixedly attached. In other embodiments the inner expandable member 103 may have a non-cylindrical cross-section, may be non-uniform in diameter, and may have tailored strut patterns to provide regions of differing radial force or flexibility.

FIG. 6A shows an isometric view of another example clot retrieval device 200. Compared to the device 100 illustrated in FIGS. 1A through 5D, the outer expandable member 202 of the clot retrieval device 200 illustrated in FIG. 6A includes multiple middle body segments 227 rather than a single middle body segment 127. At least the proximal 226 and the middle body segments 227 respectively include interconnected struts, with certain struts terminating in a distal apex 233 with no distal connecting elements, and other struts terminating in junction points. The device 200 illustrated in FIG. 6A includes three middle body segments 227. According to the present invention, a clot retrieval device including features described and illustrated herein can include one, two, three, four, five, or more middle body segments. The device 200 includes an inner expandable member 203 elongated to accommodate the additional middle body segments 227 of the outer expandable member 202.

The device 200 can include a reception space 211 between the outer expandable member 202 and inner expandable member 203 configured similarly to the reception space 111 of the device 100 illustrated in FIGS. 1A through 5C.

The device 200 can further include a proximal coil 204, distal coil 208, distal junction 209, and proximal junction 212 structured similarly as corresponding components 104, 208, 209, 212 illustrated in FIGS. 1A through 5D. The device 200 can further include a sleeve, shaft, and indicator bands structured similar to corresponding components 105, 106, 107 illustrated in FIG. 1A.

FIG. 6B shows a close-up of a portion of the clot retrieval device 200 illustrated in FIG. 6A. The portion includes a tapered connecting arm 230. The connecting arm 230 can be shaped as illustrated and described in relation to tapered connecting arms 129, 130 of the device 100 illustrated in FIGS. 1A through 5C. Connecting arms 230 can join the proximal, middle, and distal body segments 226, 227, 228 and be otherwise configured in a similar manner as connecting arms 129, 130 of the device 100 illustrated in FIGS. 1A through 5C.

FIG. 7A shows a plan view of a first side of the clot retrieval device 200. FIG. 7B shows the view clot retrieval device 200 as illustrated in FIG. 7A having the inner expandable member 203 removed for the purpose of illustration. FIG. 7C shows the view of the clot retrieval device 200 as illustrated in FIG. 7A having the outer expandable member 202 removed for the purpose of illustration.

The outer expandable member 202 of the device 200 can include a proximal struts 220 and a proximal body segment 226 structured similarly to the proximal struts 120 and proximal body segment 126 of the device 100 illustrated in FIGS. 1A through 5C. The outer expandable member 202 can include a distal body segment 228 structured similarly to the distal body segment 128 of the device 100 illustrated in FIGS. 1A through 5C. The outer expandable member 202 can include radiopaque markers 216, 221, 225 positioned and otherwise configured similarly to corresponding markers 116, 121, 125 of the device 100 illustrated in FIGS. 1A through 5C. The outer expandable member 202 can include inlet mouths 222 configured similarly to inlet mouths 122 of the device 100 illustrated in FIGS. 1A through 5C.

The inner expandable member 203 can include distal crown struts 210, interconnecting struts 231 in a tubular body portion, and proximal connecting struts 234 similar to corresponding struts 110, 131, 138 of the device 100 illustrated in FIGS. 1A through 5C. The inner expandable member 203 can be connected to an inner coil 218 configured similar to the inner coil 118 of the device 100 illustrated in FIGS. 1A through 5C.

FIG. 8A shows a plan view of a second side of the clot retrieval device illustrated in FIG. 6A, the second side viewed at 90° from the first side view illustrated in FIG. 7A. FIG. 8B shows the view clot retrieval device 200 as illustrated in FIG. 8A having the inner expandable member 203 removed for the purpose of illustration. FIG. 8C shows the view of the clot retrieval device 200 as illustrated in FIG. 8A having the outer expandable member 202 removed for the purpose of illustration.

FIG. 9 shows a linear view of the outer expandable member 202 cut along a centerline B-B indicated in FIGS. 7B and 8B and flattened. A portion of the outer expandable member 202 as indicated in FIG. 9 can be configured as illustrated in FIG. 4B and further as illustrated in FIG. 4C. For instance, radiopaque markers 221 can be staggered as illustrated in greater detail in FIG. 4B. Connecting arms 230 can be tapered and otherwise configured as arms 129 illustrated in greater detail in FIGS. 4B and 4C. Struts and joints of the outer expandable member 202 can be shaped and otherwise configured to correspond to joints and struts 144, 145, 146, 147, 150, 151 illustrated in FIGS. 4B and 4C.

FIG. 10A shows a plan view of a distal end of the clot retrieval device 200. FIG. 10B shows the view clot retrieval device 200 as illustrated in FIG. 10A having the inner expandable member 203 removed for the purpose of illustration. FIG. 10C shows the view of the clot retrieval device 200 as illustrated in FIG. 10A having the outer expandable member 202 removed for the purpose of illustration.

FIG. 11A shows an example outer expandable member 302 traversing a lumen having a 360° bend with a radius of curvature rB at the apex of the bend. Because the outer expandable member 302 closely follows the bend of the lumen, the outer expandable member has a radius of curvature that is approximately equal to the radius of curvature rB of the lumen. FIG. 11B shows a close-up of a portion of the outer expandable member 302 as indicated in FIG. 11A. The outer expandable member 302 includes tapered connecting arms 330 between body segments 327 configured similarly to the connecting arms 129, 130, 230 of the devices 100, 200 illustrated in FIGS. 1A through 10C. As shown in greater detail in FIG. 11B, the outer expandable member 302 has a curvature with a radius rA at a narrow area of the connecting arm 330 that is smaller than the overall radius of curvature rB of the outer expandable member 302 around the bend the lumen. In other words, the connecting arm 330 provides a bending point for the outer expandable member 302. The flexibility of the connecting arm 330 can allow the body segments 327 to extend juxtaposed to a lumen (e.g. the illustrated lumen and/or a blood vessel lumen) to a greater extent than a similarly structured outer expandable member having less flexible connecting arms. In one example, the outer expandable member 302 can be configured to bend with a curvature having a radius rA at the narrow area of the connecting arm 330 of approximately 0.5 millimeters (mm) or greater including 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, and 1.0 mm.

FIG. 12A shows an illustration of a portion of an example expandable member having a radiopaque marker. FIG. 12B shows a side view of the portion of the expandable member illustrated in FIG. 12A. Some or all of the markers 116, 121, 125, 216, 221, 225 of the devices illustrated and described herein can be shaped similar to the marker illustrated in FIGS. 12A and 12B.

FIGS. 13A and 13B are radiographic images of an example clot retrieval device according to aspects of the present invention. Radiopaque material in the distal coil, proximal coil, and markers appear dark in the radiographic images.

A clot retrieval device according to the teachings herein can be sized to accommodate a variety of treatment needs. Dimension such as overall length L1 of the outer expandable member, working length L2 of the device, diameter D1 of the outer expandable member D1, and diameter D2 of the inner expandable member can be measured as indicated in FIGS. 2A through 2C and 7A through 7C.

In one example device, when freely expanded, the outer expandable member can have an overall length L1 about 34 mm, a working length L2 of about 22 mm, and a diameter D1 of about 5 mm. The inner expandable member tubular body diameter D2 can measure less than the outer expandable member diameter, preferably about 1 mm and more preferably about 1.22 mm. Configured as such, the example device can be suitable for treating blood vessels having a diameter between about 1.5 mm and about 5 mm. The outer expandable member of the example device preferably includes a proximal body segment, exactly one middle body segment, and a distal body segment similar to the proximal body segment 126, middle body segment 127, and distal body segment 128 of the device 100 illustrated in FIGS. 1A through 5C.

In another example device, when freely expanded, the outer expandable member can have an overall length L1 about 49 mm, a working length L2 of about 37 mm, and a diameter D1 of about 5 mm. The inner expandable member tubular body diameter D2 can measure less than the outer expandable member diameter, preferably about 1 mm and more preferably about 1.22 mm. Configured as such, the example device can be suitable for treating blood vessels having a diameter between about 1.5 mm and about 5 mm. The outer expandable member of the example device preferably includes a proximal body segment, exactly three middle body segments, and a distal body segment similar to the proximal body segment 226, middle body segments 227, and distal body segment 228 of the device 200 illustrated in FIGS. 6A through 10C.

In another example device, when freely expanded, the outer expandable member can have an overall length L1 about 57 mm, a working length L2 of about 45 mm, and a diameter D1 of about 6.5 mm. The inner expandable member tubular body diameter D2 can measure less than the outer expandable member diameter, preferably about 1 mm and more preferably about 1.22 mm. Configured as such, the example device can be suitable for treating blood vessels having a diameter between about 1.5 mm and about 6.5 mm. The outer expandable member of the example device preferably includes a proximal body segment, exactly three middle body segments, and a distal body segment similar to the proximal body segment 226, middle body segments 227, and distal body segment 228 of the device 200 illustrated in FIGS. 6A through 10C.

In some examples, a clot retrieval device according to the teachings herein can be dimensioned such that markers on body segments (e.g. markers 121, 221 on body segments 126, 127, 128, 226, 227, 228 illustrated herein) illustrated herein can be separated in the longitudinal direction (in the direction of the longitudinal axis A-A) from one or more markers on an adjacent body segment by about 10 mm when the clot retrieval device is collapsed for delivery across a clot and can be separated by about 8 mm in the longitudinal direction when the clot retrieval device is freely expanded.

FIG. 14 illustrates an alternative distal portion of an example clot retrieval device described in greater detail in U.S. Non-Provisional Patent Publication No. 2021/0393279 and incorporated by reference as if set forth in its entirety herein.

In some examples, a clot retrieval device according to the teachings herein can have alternative geometries suitable for clot retrieval devices. For instance, the clot retrieval device can include a distal portion configured as illustrated in FIG. 14. The outer expandable member can include a distal body portion configured similar to the distal body portion 328 illustrated in FIG. 14. Alternatively, the distal portion of the clot retrieval device need not be configured to capture clot fragments and can for instance can have large cell openings or be completely open. Further, in some examples, the clot retrieval device need not include an inner body.

As discussed herein, a “patient” or “subject” can be a human or any animal. It should be appreciated that an animal can be a variety of any applicable type, including, but not limited to, mammal, veterinarian animal, livestock animal or pet-type animal, etc. As an example, the animal can be a laboratory animal specifically selected to have certain characteristics similar to a human (e.g., rat, dog, pig, monkey, or the like).

As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values ±20% of the recited value, e.g. “about 90%” may refer to the range of values from 71% to 99%. Ranges can be expressed herein as from “about” or “approximately” one particular value and/or to “about” or “approximately” another particular value. When such a range is expressed, other exemplary embodiments include from the one particular value and/or to the other particular value.

By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

In describing examples, terminology is resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the pertinent art and includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. It is also to be understood that the mention of one or more steps of a method does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Steps of a method can be performed in a different order than those described herein without departing from the scope of the disclosed technology. Similarly, it is also to be understood that the mention of one or more components in a device or system does not preclude the presence of additional components or intervening components between those components expressly identified.

The descriptions contained herein are examples of the disclosure and are not intended in any way to limit the scope of the disclosure. While particular examples of the present disclosure are described, various modifications to devices and methods can be made without departing from the scope and spirit of the disclosure. For example, while the examples described herein refer to particular components, the disclosure includes other examples utilizing various combinations of components to achieve a described functionality, utilizing alternative materials to achieve a described functionality, combining components from the various examples, combining components from the various example with known components, etc. The disclosure contemplates substitutions of component parts illustrated herein with other well-known and commercially-available products. The scope of the claims which follow are intended to include such modifications as apparent to those having skill in the pertinent art as understood according to the teachings herein. 

What is claimed is:
 1. A clot retrieval device comprising a collapsed configuration and an expanded configuration and being configured to remove a clot from a blood vessel, the clot retrieval device comprising: an inner expandable member comprising a first framework of struts that form closed cells; and an outer expandable member comprising: a second framework of struts that form closed cells larger than the closed cells of the inner expandable member and that at least partially radially surround the inner expandable member, and at least four radiopaque markers positioned around a circumference of the outer expandable member such that when the clot retrieval device is in the collapsed configuration, each of the at least four radiopaque markers is offset and staggered along a longitudinal axis of the outer expandable member to facilitate collapse of the circumference.
 2. The clot retrieval device of claim 1, wherein the at least four radiopaque markers are positioned on a first body segment of the outer expandable member, and wherein at least four additional radiopaque markers are positioned on a second body segment of the outer expandable member.
 3. The clot retrieval device of claim 2, wherein the at least four radiopaque markers facilitate visualization of a circumference of the first body segment, and wherein the at least four additional radiopaque markers facilitate visualization of a circumference of the second body segment.
 4. The clot retrieval device of claim 1, wherein the outer expandable member comprises a first body segment and a second body segment connected by two connecting arms.
 5. The clot retrieval device of claim 4, wherein at least two of the four or more radiopaque markers are aligned, in the direction of the longitudinal axis, with a respective connecting arm of the two connecting arms.
 6. The clot retrieval device of claim 4, wherein the first body segment is positioned in a proximal direction in relation to the second body segment, and wherein each of the two connecting arms respectively comprise a tapered shape being wider approximate the first body segment and narrower approximate the second body segment.
 7. The clot retrieval device of claim 4, wherein each of the two connecting arms is configured to bend with a curvature having a radius smaller than a radius of curvature of a majority of struts of the first body segment and the second body segment as the clot retrieval device is pulled proximally through a tubular vasculature comprising a bend of about 180°.
 8. The clot retrieval device of claim 4, wherein the outer expandable member further comprises three or more body segments in addition to the first body segment and the second body segment, each of the three or more body segments shaped substantially similarly to the first body segment and the second body segment, and wherein the outer expandable member comprises pairs of tapered connecting arms such that each respective pair of tapered connecting arms joins longitudinally adjacent body segments of the three or more body segments.
 9. The clot retrieval device of claim 1, wherein when the clot retrieval device is in the collapsed configuration, alternating radiopaque markers of the four or more radiopaque markers are aligned in a plane orthogonal to the longitudinal axis.
 10. The clot retrieval device of claim 1, wherein a first body segment of the outer expandable member comprises a first set of four or more radiopaque markers, wherein a second body segment of the outer expandable member comprises a second set of four or more radiopaque markers, wherein, when the clot retrieval device is in the expanded configuration, the first and second sets of four or more radiopaque markers are spaced approximately 8 millimeters apart measured in the direction of the longitudinal axis, and wherein, when the clot retrieval device is in the collapsed configuration, the first and second sets of four or more radiopaque markers are spaced approximately 10 millimeters apart measured in the direction of the longitudinal axis.
 11. The clot retrieval device of claim 1, wherein each of the four or more radiopaque markers comprises radiopaque material positioned in an eyelet.
 12. A clot retrieval device comprising a collapsed configuration and an expanded configuration and configured to remove a clot from a blood vessel, the clot retrieval device comprising: an inner expandable member comprising a first framework of struts; and an outer expandable member comprising: a second framework of struts that at least partially radially surrounds the inner expandable member, and four or more radiopaque markers affixed to the second framework of struts and positioned to indicate a circumference of the outer expandable member and further positioned such that when the clot retrieval device is in the collapsed configuration, each of the radiopaque markers is offset and staggered along a longitudinal axis of the clot retrieval device to facilitate collapse of a circumference of the outer expandable member.
 13. The clot retrieval device of claim 12, wherein the first framework of struts comprises closed cells, and wherein the second framework of struts comprises closed cells larger than the closed cells of the inner expandable member.
 14. The clot retrieval device of claim 12, wherein the outer expandable member comprises discontinuous body segments spaced apart from each other in the direction of the longitudinal axis, and wherein the four or more radiopaque markers are positioned to indicate a circumference of a body segment of the discontinuous body segments.
 15. The clot retrieval device of claim 14, wherein the body segments comprise a first body segment and a second body segment, the first body segment being positioned in a proximal direction in relation to the second body segment, wherein the outer expandable member comprises two connecting arms joining the first body segment to the second body segment, and wherein each of the two connecting arms respectively comprises a tapered shape being wider approximate the first body segment and narrower approximate the second body segment.
 16. The clot retrieval device of claim 15, wherein at least two of the four or more radiopaque markers are aligned, in the direction of the longitudinal axis, with a respective connecting arm of the two connecting arms.
 17. The clot retrieval device of claim 15, wherein the outer expandable member comprises two inlet mouths in the second framework, each of the two inlet mouths comprising a respective opening bounded by the first body segment, the second body segment, and the two connecting arms.
 18. The clot retrieval device of claim 15, wherein the first body segment comprises the four or more radiopaque markers forming a first set of markers, and wherein the second body segment comprises a second set of four or more radiopaque markers positioned to indicate a circumference of the second body segment and further positioned such that when the clot retrieval device is in the collapsed configuration, each of the radiopaque markers of the second set is offset, in relation to a longitudinal axis of the clot retrieval device to respective adjacent radiopaque markers of the second set.
 19. The clot retrieval device of claim 15, wherein the two connecting arms are positioned approximately 180° from each other about a circumference of the outer expandable member. 